The body I strap into a bikini every summer is the same body I button into a cardigan throughout autumn, the same body that sits hunched over a computer five days out of every seven, the same one that enjoys an elasticated waist. This is not the case for all women. This month, many are attempting to shrug off their bellies and slough through their dry skin to unearth their "bikini body".

The bikini body, to clarify, is like a normal body, but browner, thinner and smoother. It's a body worked on through spring to be exposed over summer, and it's a phrase that has crept stealthily into the vernacular over the past decade. This month Health & Fitness magazine offers a "bikini body" supplement, urging readers to set aside a month pre-holiday for the necessary ablutions, while Zest promises a flat stomach in six days. The fast results of the baby-food diet (devotees rumoured to include Jennifer Aniston, Cheryl Cole and Lady Gaga) invented by Tracy Anderson (Gwyneth Paltrow's personal trainer) led to Ocado's Heinz Mum's Own Creamed Porridge sales leaping by 100% at the end of May, while July's Elle introduced "fat whisperer" Mary Ascension Saulnier, a woman who "commands" fat cells to leave the bodies of clients (including Paris Hilton and Kate Hudson) before they visit the beach.

Diets (the industry of which is worth £2bn in the UK) trend all year round, but never more so than in these long, rainy months before the summer holidays when, with seasonal "Bikini Body Bootcamps", we are encouraged to consider the possibility of our weighty upper arms spoiling an otherwise perfect ocean view. This, of course, was not always the case. In the 1960s, when bikinis first became popular, they were worn to highlight your curves – today even the most beautiful women are sneered at if their belly hangs (as Marilyn Monroe's did, happily) over their knicker band. A survey by NHS Choices found 86% of women were unhappy with their "beach body". Another, by Fitness magazine, revealed that 80% believed other women were judging them on the beach, while 48% would only consider wearing a bikini after they'd lost another 20 pounds.

It's not just weight that women are expected to shed – it's hair, too: Veet claims that 74% of women think a "groomed bikini line" is the "number one must-have this beach season". When did the bikini, once a daring symbol of freedom and changing social attitudes to the body, become a threat?

I'm lying face DOWN on a pleather bench. Small electrical currents are pulsing through my upper thighs with the aim of re-sculpting my rear, and I can taste pennies – "a side-effect of the treatment", beauty consultant Bianca explains. I'm halfway through a four-hour (£430) "beach ready" menu at Richard Ward's glamorous salon in Chelsea, and on day two of the Pure Package's "Summer Stunner" food programme (three surprisingly delicious meals delivered to your office for £39.95 a day). I feel not only frighteningly detached from my own body, but a bit like I've taken on a part-time job. Because finding your bikini body takes time, not to mention money and effort.

Bianca massages my legs with the vibrating machine, to work out cellulite, and I consider the "cheatments" available. I turned down the Magnetic Melt, which harnesses "magnetic pulses" to break down fat cells. I turned down the Universal Contour Wrap, which uses "electro-stimulation straps" to reduce your silhouette by six inches. I turned down the VelaShape bottom shaper, with its infrared lights and promise of pertness. Two months of process for two weeks of confidence? The maths, to me, seems off.

Esther Fieldgrass, founder of EF Medispa (where 68% of clients visit for body tightening a month before their holidays) sees herself as a beauty pioneer. "We do find some women come to us [in search of a bikini body] with quite unrealistic expectations," she says, "hoping to come out a completely different person, rather than improving what they've got." She says the most popular bikini body treatments are dermal smoothing, laser hair removal, breast augmentation and Vaser High-Def Lipo, "a way to actually sculpt abs on to the tummy".

Marie O'Riordan, who has edited magazines including Elle and Marie Claire since 1986, has a panoramic memory of the bikini body's evolution. "I first became aware of it when I came to London from Dublin in my 20s and became friends with women who talked about sex and bodies so openly I cringed. My Damascene moment came when I had to look up cellulite in the dictionary and realised I had it. The bikini body was fixed on my radar forever."

But these were the days before Vaser Liposuction and lunch-hour boob jobs. "Back then it meant a quick epilation – courtesy of a Bic Ladies – and a two-piece that didn't crawl up your orifices," she says. "Today it involves extreme waxing, tanning, pedicuring, starving." As she is the person responsible for shaping so many women's glossies, I point out that this phenomenon reached adolescence under her editorship. "The increase in tanning and treatment advertising definitely influenced the debate," she admits. "Editorial words were swamped by ad promises." The pressure to increase circulation, she adds, encouraged the coverline every reader wanted: Get your bikini body now! The exclamation point was crucial.

But rather than changing our bodies to fit our bikinis, as has become the norm, there is still the option to buy a bikini to fit your body. This season Toast, Whistles and Bravissimo are all doing bikinis to suit even the dermal unsmoothed. Reminiscent of the swimsuits that Monroe spilled out of so glamorously, they're high waisted and wide-crotched, and the tops are structured so as to keep you buoyant even when running from waves.

In a time when perfection is seemingly only a short operation away, the commercialised freedom of the "bikini body" has become a gauge with which to measure our own insecurities. After weeks of applying the creams, I start to understand something. As I reach the end of my Pure Package diet, I realise that I'll miss it. Perhaps the point of a deadline to the bikini-body diet is simply that, post-holiday, your body becomes your own.